This invention relates to lubricating oil compositions comprising oil soluble sulfurized molybdenum sulfonate additives which are the sulfurized reaction product of a sulfonic acid compound and molybdenum halide. The reaction product is especially useful in lubricating oil compositions for reducing friction between moving parts.
Lubricating oil additives that improve operating properties of lubricating oil include dispersants, antioxidant additives, and friction modifiers that improve engine efficiency by reducing the friction between the moving parts in the engine. A large number of hydrocarbon-soluble molybdenum-containing compositions have been disclosed in recent years, including water-soluble molybdenum-amine complexes, W. F. Marzluff, Inorg. Chem. III, 345 (1964), molybdenum-oxazoline complexes, U.S. Pat. No. 4,176,074 Coupland, et al. and molybdenum lactone oxazoline complexes, U.S. Pat. No. 4,176,073 Ryer et al., molybdenum beta-keto esters, molybdenum-olefin-carbonyl complexes, molybdenum-amide complexes, molybdenum diorganophosphates, U.S. Pat. No. 4,178,258Papay, et al., molybdenum organodithiophosphates, molybdenum carboxylates, molybdenum dithiocarbamates, etc.
A series of patents issued to King and De Vries and assigned to Chevron Research Company in 1981, disclose lubricating oil compositions incorporating antioxidant molybdenum compounds, these patents being U.S. Pat. Nos. 4,259,194, 4,259,195, 4,261,843, 4,263,152, 4,265,773, 4,272,387, 4,283,295, and 4,285,822. The inventors state that the precise molecular formula of these molecular compounds is not known, but they are believed to be compounds with molybdenum oxides or sulfides complexed by or the salt of one or more nitrogen atoms from a basic nitrogen-containing composition (such as, e.g., succinimide, carboxylic acid and Mannich bases) used to prepare the lubricant. A polar promotor to facilitate the interaction between the acidic molybdenum compound and basic nitrogen compound may be used, preferably ethylene glycol or water.
U.S. Pat. No. 3,047,500, Matson, discloses what the patentees believe to be a molybdenum disulfide formed in situ as a result of the interaction of a molybdenum phenolate and an oil-soluble organic sulfur compound. These two ingredients are added to a lubricant for extreme pressure protection, there being no chemical interaction between the molybdenum and sulfur until substantial heat has been generated on the work surface to produce the molybdenum sulfide. U.S. Pat. No. 4,266,945, Karn, discloses a friction modifying lubricant prepared by the reaction of an acid of molybdenum with a phenol or aldehyde condensation product and a primary or secondary amine. The compositions are stated to be especially useful when combined with active sulfur and an oil-soluble dispersant. U.S. Pat. No. 4,202,781, Sabol, et al., discloses a method of preparing a molybdenum phosphosulfurized hydrocarbon composition, the composition being useful as an oxidation inhibitor and friction modifier for lubricants of internal combustion engines. The reaction disclosed produces stable molybdenum-containing compositions without the use of high temperatures, ether-complexing solvents or hydrogen peroxide.
The molybdenum compounds produced by the methods of the above-noted patents, all of which are expressly incorporated by reference herein, potentially suffer from either economic inefficiencies or from changing product requirements. For instance, at least one major U.S. automobile manufacturer has specified a maximum level of 0.11 per cent phosphorus in motor oils used in internal combustion engines in 1983 and thereafter. Most commercially available oil-soluble molybdenum additives having antifriction properties in lubricating oil contain phosphorus in the form of phosphosulfurized hydrocarbons or thiophosphates. However, the most effective anti-wear additive commonly used in lubricating oils is a zinc-phosphorus composition, such as zinc dithiophosphate, which is useful in amounts to potentially account for the entire phosphorus "allotment" in lubricating oil. Therefore, a need exists for a molybdenum-containing additive which provides friction reduction properties at low cost without the use of phosphorus.